Hard-wired sensors for picking up medical or physiological data such as ECGs, SpO2 and blood pressure have long been known. In more recent times, efforts have been devoted to linking sensors of this kind to one another, or to a data sink, without the use of wires or cables by means of a wireless communications network. In the world of those skilled in the art, wireless sensor networks are known by the name of body area networks (BAN). What happens in this case is that physiological data relating to a patient is picked up by a sensor and is transmitted by means of a short-range RF service to a patient monitor situated a short distance away or to a wireless network that is installed in the hospital. What is advantageous in this case is that, as a result of the use of wireless sensors, there are considerably fewer cables for the patient to support on his or her body. In the past, conventional sensors had transmitted their data to a patient monitor via respective cables. Dispensing with this large number of cables gives the patient greater freedom of movement. It is for example easily possible in this way for the patient to get up from his or her bed. However, account has to be taken in this case of the fact that the network needs to supply data to the patient information system with high reliability even in the event of the patient getting up or walking around in the hospital.
Standard IEEE 802.15.4 provides the specifications for a body area network (BAN). This standard describes in particular the physical layer and the medium access control layer of a network of this kind. Under the standard there is specified a communications link in the form of a channel that is divided into superframes. The superframes comprise a plurality of time slots. They begin with and are synchronized by a beacon dataset. The superframes can be subdivided into active and inactive parts, it then being possible for transceiver devices to switch to an energy-saving mode during the inactive part.
The above-mentioned standard describes a short range RF technique and it was developed for typical distances between the transceiver devices of between 0.2 m and 10 m.
For many applications in the field of wireless sensors, a primary consideration is low energy consumption by the transceiver devices. In this way, the present applicant for example is developing a wireless communications system for monitoring the state of health of patients with the help of a plurality of biomedical sensors. A variety of biomedical sensors are linked in to the on-body wireless network. The transceiver devices communicate with one another and with the world around them in order to pick up and transmit data on a patient's state of health. Each transceiver device includes one or more sensors and a processing unit and a communications unit. The communications unit is also referred to in the present text as a transceiver.
The supply of energy to the transceiver device of a network of this kind needs to be ensured, for a number of weeks or months, by means of batteries of as small a type as possible without the need for the batteries to be changed or recharged. The limited amount of energy stored in the battery has to be enough to cover the operation of the sensors, i.e. the picking up of measured values and the communication via the transceiver.
An object underlying the present invention is to specify an arrangement and a process of the kind detailed in the opening paragraph that, by optimizing the conditions of transmission and reception, reduce the amount of energy required to operate the transceiver both in the transmitting mode and in the receiving mode.
In accordance with the invention, this object is achieved by a device of the kind mentioned in the opening paragraph by virtue of the features of claim 1. The invention comprises a transceiver device that processes a medium access control (MAC) protocol of a transceiver. The transceiver has a first antenna system for on-body communications and a further, second, antenna system for off-body communications.
The transceiver device for on-body communications is also able to reserve one or more data payloads and, at this time, to allocate the first antenna system for on-body communications to the transceiver.
Furthermore, the transceiver device is also able to reserve one or more data payloads for off-body communications and, in this interval of time, to allocate the second antenna system for off-body communications to the transceiver.
An advantageous result of this is that optimally adapted antenna systems are available for, respectively, communications close to the body and communications distant from the body. By the assigning of on-body data payloads and off-body data payloads, it is possible to reduce collisions within the network that are caused by non-optimum selection of the antenna systems.
In accordance with the invention, the match between an optimum antenna polar diagram and the rights of use to the channel advantageously produces optimized data throughput on the radio channel. Hand in hand with this there is a reduction in the stress on the patient caused by radio frequency radiation. Another advantageous result is that, because of the optimized way in which the antenna systems of the transceiver device are trained on the destination to which messages are to be transmitted, only low transmitting power is required. What is also an advantageous result is the fact that, because of the optimized granting of rights of use to users on the radio channel, the respective transceivers can be operated, at times, in the energy-saving sleep mode. A more effective use of energy is achieved in this way and this improves the battery-based endurance of the sensors.
What is meant by an antenna system is an arrangement that comprises at least one antenna. However, what may be also present in an antenna system, as well as the antenna, are devices that change the polar diagram of an antenna such for example as switches, relays, attenuators, phase shifters, etc.
The invention also covers a device as specified above in which a network coordinator provides time slots for on-body communications and time slots for off-body communications in a superframe. An advantageous result of this is that, because of the allocation of time slots, less work has to be done to administer the radio channel. The amount of protocol traffic on the radio channel thus goes down and in return the throughput of data goes up.
The invention also makes provision for a device as specified above in which synchronization of the data payloads for on-body communications and/or off-body communications is performed by means of at least one beacon payload that is generated by the network coordinator.
In one embodiment, each transceiver device on the network may request time slots for communications with on-body devices or off-body devices, as the case may be, from the network coordinator, with the network coordinator granting the network users rights of use for time slots, for transmission and reception, by means of a beacon payload. As well as this, the network coordinator may also provide, in a superframe, time slots in the form of contention access periods (CAP) or in the form of guaranteed time slots (GTS), each of these for on-body or off-body communications.
What is meant by contention access is a method of accessing a channel in which each user observes the channel as a receiver and only changes to transmitting when a quiescent pause has occurred, i.e. when a signal from another user is not having to be received onto the channel.
Similarly, what is meant by a contention access period is a period of time in which the above-mentioned method of accessing a channel is being carried out.
What is meant by the assignment of guaranteed time slots (GTS) is a method of accessing a channel in which at least one user is granted an exclusive right to use the channel for the period of time in question.
An advantageous result of this is fewer collisions when access is being sought to the radio channel, because of the guaranteed time slots. There is an increase in the throughput of data due to the granting of guaranteed rights of use for communications between individual transceivers. What is more, all the transceivers do not have to be ready to receive all the time and instead some of the receivers may be operated in the energy-saving sleep mode, the consequence of which is a considerable reduction in the energy consumption of the individual transceivers.
In another preferred embodiment of the invention, a network coordinator that is arranged on-body transmits the beacon payload in parallel by means of the first and second antenna systems.
An advantageous result of this is that any device on the network is able to perform the function of network coordinator and that even devices arranged on-body make provision for optimum emission of the beacon payload.
In a further embodiment, the invention also makes provision for a converter to have the first and at least one other antenna system, with the further antenna system or systems being intended for communications links conforming to a mid range RF link standard.
An advantageous result of this is that a link with the patient's BAN can be established or continuously maintained at any time regardless of where the patient is, i.e. it does not matter whether the patient is in bed or walking round the hospital.
The invention also provides a system for wireless communications between at least one transceiver device, comprising
transceiver devices arranged on the patient's body,
transceiving units positioned off-body.
What is meant by a transceiver device is a unit that also includes, as well as a transceiving unit, other functional units such for example as a sensor unit, a display, a processor and a memory but also antennas, switches, measuring, control and regulating devices, etc. Examples of a transceiver device of this kind are a hub, a gateway, a protocol converter, a patient monitor, a sensor, etc.
What is meant by a transceiving unit is a device that generates, conducts, processes or switches radio frequency signals, such for example as a transmitter, a receiver, a transceiver, an antenna switch, a cable, a waveguide, a relay, an electronic circuit, etc.
The invention also provides a system as specified above in which the said system has a transceiver device according to the invention that performs the function of a converter. This converter serves to change data between a radio link standard for on-body/off-body communications to any desired other standard for radio links, and/or it serves to translate between the protocol for on-body or off-body communications and other radio services. If a short range RF link and a mid range RF system link exist simultaneously, this ensures that the BAN is linked into the system redundantly. What is advantageous in this case is that if either of the two links fails or suffers interference or disruptions, whichever is the other link is still available.
The invention also provides a system as specified above in which any transceiver device on the network is able to assume the function of network coordinator, and in which the function of network coordinator is assigned to that transceiver device on the network that is switched on first.
The invention also provides a system as specified above for exchanging data between a sensor that is arranged on a patient and a patient information center, comprising:
an off-body communications link via a patient monitor, or
an on-body communications link to a converter and the exchange of data by means of the converter over a mid range RF link made via the third antenna system. An advantageous result of this is that, because the selection of the antenna system is optimized regardless of the RF link, it is guaranteed that behavior in respect of electromagnetic environmental compatibility, energy efficiency and data throughput will be optimum no matter where the patient is.
What is more, the invention also provides a MAC protocol process in which a transceiver device divides a transmission channel into superframes that follow one another in time. The superframes comprise at least a beacon payload, a data payload for on-body communications and a data payload for off-body communications. What is meant by a MAC protocol process is the process of controlling media access in ISO-OSI layer 2. The MAC layer is the second layer from the bottom and comprises network protocols and components that regulate how a plurality of processors apportion the physical transmission medium of which they make shared use.
The beacon payload is generated by the network coordinator. The transmission range for data payloads for on-body communications is from 0 to 20 m, and preferably 0 to 2 m, an antenna system for on-body communications being used during the period of time occupied by the data payloads for on-body communications. The transmission range for data payloads for off-body communications is from 0 to 100 m, and preferably 0 to 15 m, an antenna system for off-body communications being used for this purpose.
The invention also provides a MAC protocol process as specified above in which the MAC protocol process makes provision for a transceiver device as the network coordinator, the network coordinator coordinating the on-body and off-body radio traffic by allocating time slots by means of the beacon payload.
The invention also provides a MAC protocol process as specified above in which each transceiver device divides the superframes into as many intervals of time for data payloads as desired, but preferably into 16 thereof.
In the superframe,
one or more data payloads are reserved for on-body communications, the antenna system that is assigned to the transceiver being the first one in this case, and/or
one or more data payloads are reserved for off-body communications, the antenna system that is assigned to the transceiver being the second one in this case.
An advantageous result of this is that, because of the allocation of the intervals of time and the allocation of the length of the data payloads, there is great flexibility in the selecting of data throughout, the selecting of the amount of data to be transmitted and the selecting of the time for the measurement of data.
The invention also provides a MAC protocol process as specified above in which a transceiver device serves as a protocol converter, in the form of a hub, bridge, or gateway for example, between the protocol process used in the on-body or off-body communications, as the case may be, and some other protocol process. As well as having the advantages mentioned above, the provision of a protocol converter also has that of making it possible for the most advantageous protocol process for the conversion of data to be selected on a radio service.